In a culture of passive entertainment, the writing of fanfiction is a subversive act. It transforms the process of consuming entertainment into an active, dynamic experience. Granted, that doesn't mean the output is always good, or even readable. But fans who take the characters, plots, and settings that they love and make them their own are doing more than just indulging in escapism. They are turning the expectations of corporate creativity upside-down and declaring that the starship Enterprise - or the FBI, or the strange little suburb called Sunnydale - is their playground too. And if fanfiction is subversive, homoerotic fanfiction is doubly so.
'They' call it slash. It evolved out of the fandom for the original Star Trek series, when some fans - mostly straight women - thought they saw gay subtext between Kirk and Spock that the show could never actually portray.
Some thirty years later, slash has expanded until there is a slash fandom for almost every science fiction series you can think of, and many non-SF ones as well. There is slash based on the characters in books or movies, or highly obscure shows, often called rareslash. There is slash based on real people, always a controversial topic, such as band members or famous actors. And, of course, the popular television series slashers are still going strong.
The word slash comes from the '/' used between the initials of each character, in what is called the pairing. K/S - Kirk-slash-Spock. Most of the pairings involve two men sexually or romantically involved, but female pairings are also out there. Most of the stories continue to be written by straight women. Slash is, within the generally somewhat homophobic and male-oriented SF community, a major women's community. Lesbians, bisexuals, and gay men also write it, and you can even find a few straight men.
These days The X-Files gives all the Star Trek series combined a run for their money, and Buffy the Vampire Slayer has a not-inconsiderable base behind it as well.
The differences between slash and 'genfic' - general, non-adult fanfiction - are more than just topical. Slash, many are quick to say, is not pornography, it is erotica. While the distinction between those areas is vague, it is true that slash fiction tends to be more thoughtful and relationship driven than all-out smut is. Relationships are carefully developed, sex comes after pages of doubt and tension, or as a part of a loving, stable partnership. While some slash is purely PWP - plot-what-plot?, the fanficcer's term for just the smut, please - the majority is not.
Why do slashers do it? Some have said it is a feminist act: women taking control of men in a way they cannot in real life (or simply being unable to find female characters they can relate to). Others think it is a thrill of taboo-breaking that drives them on.
Slashers themselves have engaged in a lot of debate, over the years, about the meaning of it all. But these days, most slashers would answer the question "Why do you do it?" with a simple reply: "Because we like it, that's why, and that's enough."